He had been:
-Kidnapped and trained for a year by Piccolo
-Fought Nappa, someone with two times his power level, and nearly had his face smashed into a pulp
-Travelled to a far off planet not yet discovered by humans
-Got his neck snapped by Recoome and was paralyzed traumatically on the edge of death
-Fought with Frieza in multiple forms, at one point nearly gaining the upper hand, at most points again on the edge of death
-Mastered both Piccolo and Goku's energy techniques, Masenko and Kamehameha
-Turned Super Saiyan 1 and then 2
-Killed Cell and saved the world
In contrast by the time Goku hit 12:
-He was living with a dragon ball that he thought was his grandfather
-Patting Bulma to see if she had a penis
-And barely being able to count to 12
-Kidnapped and trained for a year by Piccolo
-Fought Nappa, someone with two times his power level, and nearly had his face smashed into a pulp
-Travelled to a far off planet not yet discovered by humans
-Got his neck snapped by Recoome and was paralyzed traumatically on the edge of death
-Fought with Frieza in multiple forms, at one point nearly gaining the upper hand, at most points again on the edge of death
-Mastered both Piccolo and Goku's energy techniques, Masenko and Kamehameha
-Turned Super Saiyan 1 and then 2
-Killed Cell and saved the world
In contrast by the time Goku hit 12:
-He was living with a dragon ball that he thought was his grandfather
-Patting Bulma to see if she had a penis
-And barely being able to count to 12
damn...doesnt explain why he was the lamest 17 year old on earth though 






